Align sync auth with other SDKs

[kneth]

The current auth API is hard to new users to understand and use. I suggest that Realm JS is aligned with the other Realm SDKs.

• The current methods (registerWithProvider, login) are deprecated and to be removed as soon as possible.
• A new classRealm.Sync.Credentials is added. It will interface supported 3rd party provides, e.g., JWT, Google and Facebook.
• Methods for logging in and and logging out are added to Realm.Sync.User.

An example:

credentials = Realm.Sync.Credentials.facebook(getFacebookToken())
Realm.Sync.User.login(credentials, "http://objectserver.realm.io/auth").then(user => {
    // user is now logged and and can open a Realm
}).catch(error => {
    // an error has occurred and be handled
})

[nirinchev]

This could be related: #1571

[bigfish24]

This is a good discussion to have since I think we should simplify the auth to just:

1. Username/password
2. JWT (custom)
3. Anonymous

I think just having 1 method like authenticate or login would be sufficient to pass a credential and return a user.

[nirinchev]

I'm not sure about that - if the goal is to allow people to bootstrap quickly, the JWT flow isn't exactly ideal. It requires writing code to issue my own tokens and hosting this on another service. If I already have that in place, great, but if I don't, it's fairly annoying.

[kneth]

@bigfish24 I would assume that Facebook and Google auth are important in a React Native context?

@nirinchev Will credentials = Realm.Sync.Credentials.JWT(getJWTToken()) make it harder to get started with JWT?

[nirinchev]

What would getJWTToken do? I think the main obstacle for getting started with JWT is simply the fact you have to host your own server/service that exposes some http API to login and returns a signed JWT. None of that is hard per se, it's more of a hassle to do it - you have to sign up with a cloud provider, provision a server or an application that hosts your logic, provision ssl certificates, etc. In any case, that doesn't tie directly to our SDKs - once you have that token issued, passing it to Realm is fairly easy and the Credentials-based API is straightforward enough and aligned with other SDKs.

[kneth]

getJWTToken() is the main obstacle you refer to 😄 - I just leave it as an exercise for the reader.

I agree that we shouldn't duplicate effort (#1571).

[kneth]

I close this as #2002 has been merged and released.